php-ai / php-ml

                return function ($x, $y) {

                    return Matrix::dot($x, $y)[0];

                };

            case self::KERNEL_RBF:

                // k(x,y)=exp(-γ.|x-y|) where |..| is Euclidean distance

                $dist = new Euclidean();

                return function ($x, $y) use ($dist) {

                    return exp(-$this->gamma * $dist->sqDistance($x, $y));

                };

            case self::KERNEL_SIGMOID:

                // k(x,y)=tanh(γ.xT.y+c0) where c0=1

                    return tanh($this->gamma * $res);

                };

            case self::KERNEL_LAPLACIAN:

                // k(x,y)=exp(-γ.|x-y|) where |..| is Manhattan distance

                $dist = new Manhattan();

                return function ($x, $y) use ($dist) {

                    return exp(-$this->gamma * $dist->distance($x, $y));

                };

        }

    }